Various types of particulates, such as granular or dry powdered material, typically are shipped in reduced, manageable quantities in nonrigid containers or bags made of fabric, paper, or other suitable material Normally, these bags are filled by automatic packaging machines, the bags being referred to as "valve bags" since at least one of their ends includes some form of a valve or filling opening. The valve is structured to accommodate a filling spout or tube extending from the packaging machine and inserted into the valve orifice so that material can be transported by the machine from a storage container or hopper into the bag. These valves can be formed by a specific folding of the end flaps of the bag or can be formed as a separate sleeve integral with the end of the bag.
In order to prevent leakage during shipping and handling of the bag, it is desirable to use a valve size that is as small as possible so that the valve or opening can be sealed easily and can be maintained in a sealed condition, even during rough handling of the bag. The use of a small valve, however, necessitates the use of a small filling tube which increases the time required for filling the bag due to the small displacement of the tube. Although the flow rate through a small tube can be increased, its top speed is limited by the speed at which particulate material can be fed to the small tube. When a hopper or similar material supply means is employed, the top speed through the small tube is normally limited by the speed at which particulate material falls within the hopper due to the force of gravity. If the flow rate through the small tube exceeds the rate of gravitational material flow in the hopper, the displacement of the tube will be reduced and undesirable cavitation will occur within the hopper.
Automatic packaging machines for filling a valve bag with granular or dry powdered material from a hopper that are designed to decrease filling time by accelerating the flow rate of the material through a filling tube are known. One example of such a machine is disclosed in U.S. Pat. No. 2,279,640 which discloses a two-stage auger that is used in conjunction with a hopper and a filling tube. The hopper is filled with a predetermined measured quantity of material that is to be conveyed by the auger into the bag through the valve.
The two-stage auger includes a first portion of flights dimensioned and pitched for low speed movement of the material in the hopper and a second portion of flights dimensioned and pitched for high speed movement of the material through the filling tube. The first portion of flights is formed along the exterior of a first hollow shaft. A second shaft extends through and protrudes from opposite ends of the first hollow shaft. The second portion of flights is formed along the exterior of the second shaft on one of the portions of the second shaft protruding from the first hollow shaft. To rotationally seat the second shaft with respect to the first hollow shaft, ball bearings are positioned on either end of the first hollow shaft. To provide variable speeds between the two shafts, the two shafts are driven at their ends opposite the flights on the second shaft. Accordingly, with this type of machine the filling tube can be small to fit through the bag valve and the material flow rate in the tube can be increased to enable decreased bag filling time.
Such existing two-stage augers normally are effective only when a premeasured quantity of particulate material is supplied within the hopper. Even then, it is inevitable that precise amounts of material are not conveyed into the bag since some material will remain between flights as well as within the bottom of the hopper or the filling tube. Additionally, the transition between flights is so abrupt that the flow of the material is hampered, material can be broken down, and material can lodge in the space between the auger shafts to foul the rotational bearings.
It is also known to provide an automatic packaging machine for filling a valve bag with an automatic weighing system. Such a system typically includes an enlarged hopper having a bag filling means, a filling tube, a weighing mechanism, a bag support mounted on the weighing mechanism, and a frame which supports these items. In operation, the valve of the bag is placed on the filling spout and the bag is clamped in place on the bag support. Material is provided within the hopper and the filling means is activated to convey a portion of the material from the hopper into the bag. When the quantity of material within the bag attains a prescribed weight, the weighing mechanism, through appropriate controls, stops the filling means. The filled bag is then unclamped from the bag support and removed from the filling tube for subsequent sealing and transport.
If a two-stage auger is used with a weighing system, material would be present constantly within the hopper as well as along the flights and within the filling tube. Accordingly material could lodge more easily between the auger shafts to foul the rotational bearings even more than the two-stage augers that convey a premeasured quantity of material. Moreover, it would be even more important that a smooth transition of material flow be established between the two portions of flights especially during initial start up and stopping of the auger.
It would therefore be advantageous to provide an automatic packaging system having a two-stage auger for conveying granular or dry powdered material from an enlarged hopper to a valve bag that can be used in conjunction with a weighing mechanism that can fill a valved bag automatically with a precise amount of material. Another desirable advantage would be to provide such an automatic packaging system that includes means for independently adjusting the speeds between the two sets of auger flights to reduce undesirable material flow conditions within the system that is also capable of filling a valve bag in a decreased filling time, which does not become fouled with particulate material, and which provides a smooth transition for the material flow between the two sets of auger flights.